1. Field of the Invention
The present invention relates to an Archimedean screw apparatus for use either in power generation or in the pumping or conveying of fluid material.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Conventionally, a modern Archimedean screw apparatus comprises a screw body having a rotatable shaft around which is secured one or more helical flights. The shaft is suspended at its ends between bearings, typically a drive-end bearing and a non drive-end bearing, in a close fitting trough and a small clearance is left between the flights and the trough or a liner located in the trough. In a pumping apparatus, the trough is either horizontal or inclined and the shaft is driven to pump material along the trough, from the bottom to the top if it is inclined. In contrast, in power generation the trough is inclined and fluid flows down the trough under gravity to rotate the screw body, which is linked to a generator. Power to or torque from the screw body is therefore transmitted by the shaft and it is important that the length and strength of the shaft are chosen so that the screw body is sufficiently strong to remain suspended without serious bending or deflection, which would create undue stresses in the screw body and cause contact with the trough. Hence, the longer the screw body the stronger it needs to be to withstand the bending moments to which it is subjected.